I have 3/4 double bass and his strings lenght is 108cm.
When I play the low positions on the E string it's buzz very hard.
The string hit the wood underneath.
it's seems like the string don't have enough tension.
I tried to put a new pirocore medium and it's still buzz.
I have a new fingerboard with flat fingerboard behind E and
rounded behind the other strings.
when the string buzz it's hit the fingerboard almost it the end of the flat fingerboard (near the D area).
It's not your string's problem. It's your luthier. He/she has obviously had little experience in dealing with basses. I know lots of violin luthiers who claim they know how to fix basses but don't. Make sure you give your bass to a luthier who has actually studied how to set up a bass and you will find what wonderful things a person can do to your bass just tweaking things you don't normally even notice.
Agreed. Sounds like there is inadequate camber (scoop) on the E string side. The beveled fingerboard is easier to set-up to play cleanly. No, you do not need a round board.
Anything is possible but it sounds like a flat board rather than a board with good relief. d_lahish if you can put a yard stick (preferably aluminum) on the board and tell us what you see. OR just hold down the E string on both ends of the board as if it were a straight edge. How much space is apparent and how does it change from end to end????
I am having a similar problem and my string height on teh E is quite high, to match the top gut strings. My luthier says that the camber is fine, the nut is fine and that he wouldn't plane the fingerboard down because there isn't enough wood. A new fat fingerboard would do the trick. he says it's quite likely that because the board is fairly think (Christopher bass) the neck is bowing forward where it shouldn't be. The buzz occurs mistly in half position and when the string is played open.
Low tension problem, E string buzz 
